4 files changed, 180 insertions, 0 deletions
diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..57872d0
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1 @@
+/vendor/
diff --git a/composer.json b/composer.json
new file mode 100644
index 0000000..c15582f
--- /dev/null
+++ b/composer.json
@@ -0,0 +1,18 @@
+{
+    "name": "askonomm/validator",
+    "description": "A modular validation library with sane default",
+    "type": "library",
+    "license": "MIT",
+    "autoload": {
+        "psr-4": {
+            "Askonomm\\Validator\\": "src/"
+        }
+    },
+    "authors": [
+        {
+            "name": "Asko Nomm",
+            "email": "asko@bien.ee"
+        }
+    ],
+    "require": {}
+}
diff --git a/src/Validator.php b/src/Validator.php
new file mode 100644
index 0000000..8d91bb9
--- /dev/null
+++ b/src/Validator.php
@@ -0,0 +1,111 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Askonomm\Validator;
+
+/**
+ * The Validator class takes in an array of fields and 
+ * an array of validators. Each field must have a key 
+ * that matches the validator key so that `Validator` class
+ * would know how to connect the two, and the value of the each 
+ * validator is a string that consists of rules separated by the 
+ * `|` character.
+ * 
+ * Example use:
+ * 
+ * ```php
+ * $fields = ['email' => 'test@example.com'];
+ * $validators = ['email' => 'required|email'];
+ * $validator = new Validator($fields, $validators);
+ * 
+ * if ($validator->fails()) {
+ *  return $validator->errors();
+ * }
+ * ```
+ * 
+ * @author Asko Nomm <asko@bien.ee>
+ */
+class Validator
+{
+    private array $errors = [];
+
+    public function __construct(
+        private array $fields,
+        private array $validators,
+        array $rules = [],
+    ) {
+        if (empty($rules)) {
+            $this->rules = $this->defaultRules();
+        }
+
+        $this->validate();
+    }
+
+    public function defaultRules(): array
+    {
+        return [
+            'len' => ValidatorRules::len(),
+            'email' => ValidatorRules::email(),
+            'required' => ValidatorRules::required(),
+        ];
+    }
+
+    /**
+     * Runs `$this->validators` over `$this->fields` to construct 
+     * potential errors that will be stored as an array of strings 
+     * in `$this->errors`.
+     *
+     * @return void
+     */
+    private function validate(): void
+    {
+        foreach ($this->validators as $field => $validator) {
+            $value = $this->fields[$field];
+
+            foreach (explode('|', $validator) as $item) {
+                if (str_contains($item, ':')) {
+                    [$name, $modifier] = explode(':', $item);
+
+                    if (!$this->rules[$name]['validates']($value, $modifier)) {
+                        $this->errors[] = $this->rules[$name]['error']($field, $modifier);
+                    }
+                } else {
+
+                    if (!$this->rules[$item]['validates']($value)) {
+                        $this->errors[] = $this->rules[$item]['error']($field);
+                    }
+                }
+            }
+        }
+    }
+
+    /**
+     * Returns a boolean `true` if there have been any errors.
+     * Returns `false` otherwise.
+     *
+     * @return boolean
+     */
+    public function fails(): bool
+    {
+        return count($this->errors) !== 0;
+    }
+
+    /**
+     * Returns an array of strings where each string 
+     * is a single error that happened during validation.
+     */
+    public function errors(): array
+    {
+        return $this->errors;
+    }
+
+    public function firstError(): string
+    {
+        if (count($this->errors) > 0) {
+            return $this->errors[0];
+        }
+
+        return '';
+    }
+}
diff --git a/src/ValidatorRules.php b/src/ValidatorRules.php
new file mode 100644
index 0000000..d3599e0
--- /dev/null
+++ b/src/ValidatorRules.php
@@ -0,0 +1,50 @@
+<?php
+
+namespace Askonomm\Validator;
+
+class ValidatorRules
+{
+    public static function len(): array
+    {
+        return [
+            'error' => function (string $field, mixed $modifier = 0): string {
+                return "{$field} is shorter than the required ${modifier} characters.";
+            },
+            'validates' => function (string $value, mixed $modifier = 0): bool {
+                if (!isset($value) || strlen($value) < (int) $modifier) {
+                    return false;
+                }
+
+                return true;
+            }
+        ];
+    }
+
+    public static function email(): array
+    {
+        return [
+            'error' => function (string $field): string {
+                return "${field} is not a valid e-mail address.";
+            },
+            'validates' => function (string $value): bool {
+                if (!isset($value) || !filter_var($value, FILTER_VALIDATE_EMAIL)) {
+                    return false;
+                }
+
+                return true;
+            }
+        ];
+    }
+
+    public static function required(): array
+    {
+        return [
+            'error' => function (string $field): string {
+                return "${field} is required.";
+            },
+            'validates' => function (string $value): bool {
+                return isset($value) && $value !== '';
+            }
+        ];
+    }
+}